1. Field of the Invention
This invention relates to "clear pipe" communication networks meaning the nodes and links handle a variety of data frame types, depending on their communication protocols, such as Token Ring, Ethernet, FDDI or ATM. More particularly, this invention relates to node/link interface adapters at nodes which include switching nodes and end nodes. The adapters identify data frame type, and adapt the node/link adapter operative elements to handle the various types of data frames as they travel through the network.
2. Description of Related Art
In data processing communication networks within a campus of buildings, the predominant communication protocols are Token Ring, FDDI, and Ethernet. There is also a new communication protocol known as ATM (Asynchronous Transfer Mode). The data frame format used by each of these communication protocols is shown in FIGS. 1A, 1B, 1C and 1D.
In FIG. 1A, the Token Ring data frame format begins with a Start Delimiter SD which is an octet (8 bits). The SD is followed by the Access Control AC and the Frame Control FC which are also octets. The SD and AC are referred to together as the Start-of-Frame Sequence SFS. After the FC, there is the Destination Address DA and Source Address and the optional Routing Information RI. Each of the addresses is 6 octets in length. The Information INFO, or data carried by the frame, follows the routing information, and may be 0 (zero) to many octets in length. After the INFO comes the Frame Check Sequence FCS. The FCS is 4 octets long, and is used to check the data frame from FC through FCS for errors in transmission. The Token Ring data frame ends with End Delimiter ED and the Frame Status FS which are referred to as the End-of-Frame Sequence EFS. The content of the frame between Start Delimiter SD and End Delimiter ED is referred to herein as payload.
The FDDI data frame format is shown in FIG. 1B where the SFS (Start of Frame Sequence) contains a preamble followed by SD (Start Delimiter). The payload includes in sequence, the Frame Control FC, the Destination Address DA, the Source Address SA, the Information INFO, and the Frame Check Sequence FCS. In FDDI, the FCS covers the payload. The End-of-Frame Sequence EFS includes the End Delimiter ED and the Frame Status FS.
The Ethernet data frame format in FIG. 1C also begins with a Preamble and Start Delimiter SFD. The payload follows the SFD, and contains in sequence the Destination Address, the Source Address, the frame Length, the Data, the PAD (0's placed in the frame if necessary to bring the frame to the minimum required size), and the Frame Check Sequence. There is no End Delimiter since the frame Length defines the end of the frame.
In FIG. 1D, the ATM cell structure or frame is shown. It is a very simple structure having only two parts, Header and Information. The Header contains virtual path and channel identifiers, and various control bits. The virtual path and channel identifiers are used to route an ATM cell through an ATM network from source to destination.
The two most significant problems in handling all of these data frame types in one network are (1) how to find the destination address in each frame as the frame is processed at each node, switch port or work station, and (2) how to match the transmission rate of the frame to data rate of the node.